EXPERIMENTAL MORPHOGENESIS 163 



important in themselves, would not disclose anything 

 fundamentally new, and so we may close the subject with 

 the remark that nothing can show better than the fact 

 of the equifinality of restitutions how absolutely inadequate 

 all our scientific conceptions are when confronted with the 

 actual phenomena of life itself. By analysis we have found 

 differences of potencies, according as they are simple or 

 complex ; by analysis we have found differences of " systems," 

 differences of means, and indeed we were glad to be able to 

 formulate these differences as strictly as possible : but now 

 we see how, in defiance of our discriminations, one and the 

 same species of animals behaves now like one sort of our 

 " systems," and now like the other ; how it uses now one 

 sort of " potencies/'' now another. 



But even if it is granted that, in the presence of such 

 phenomena of life, our endeavour seems to be like a child's 

 play on the shores of the ocean, I do not see any other 

 way for us to go, so long, at least, as our goal is human 

 science that is, a study of facts as demanded by our mental 

 organisation. 



REMARKS ON " RETRO-DIFFERENTIATION ' 



We shall finish this part of our studies by mentioning 

 a little more explicitly one fundamental fact which has 

 already entered incidentally into our considerations, viz. 

 retro- or back-differentiation} We know that it occurs in 

 Clavellina and in Tubularia ; we may add that it also 

 happens in Hydra, and that in the flatworm Planaria the 

 pharynx, if it is too large for a piece that is cut out, 



1 " Retro "-differentiation, of course, is not " Re "-differentiation (" Um- 

 differenzierung," see p. Ill), though it may help it to occur. 



